Function p_cansignal

freebsd/kern/kern_prot.c:1570–1601

- * Determine whether td may deliver the specified signal to p. * Returns: 0 for permitted, an errno value otherwise * Locks: Sufficient locks to protect various components of td and p * must be held. td must be curthread, and a lock must be * held for p. * References: td and p must be valid for the lifetime of the call */

 * References: td and p must be valid for the lifetime of the call
 */
int
p_cansignal(struct thread *td, struct proc *p, int signum)
{

	KASSERT(td == curthread, ("%s: td not curthread", __func__));
	PROC_LOCK_ASSERT(p, MA_OWNED);
	if (td->td_proc == p)
		return (0);

	/*
	 * UNIX signalling semantics require that processes in the same
	 * session always be able to deliver SIGCONT to one another,
	 * overriding the remaining protections.
	 */
	/* XXX: This will require an additional lock of some sort. */
	if (signum == SIGCONT && td->td_proc->p_session == p->p_session)
		return (0);
	/*
	 * Some compat layers use SIGTHR and higher signals for
	 * communication between different kernel threads of the same
	 * process, so that they expect that it's always possible to
	 * deliver them, even for suid applications where cr_cansignal() can
	 * deny such ability for security consideration.  It should be
	 * pretty safe to do since the only way to create two processes
	 * with the same p_leader is via rfork(2).
	 */
	if (td->td_proc->p_leader != NULL && signum >= SIGTHR &&
	    signum < SIGTHR + 4 && td->td_proc->p_leader == p->p_leader)
		return (0);

	return (cr_cansignal(td->td_ucred, p, signum));
}

/*-
 * Determine whether td may reschedule p.